High-power fibre lasers

Journal name:
Nature Photonics
Volume:
7,
Pages:
861–867
Year published:
DOI:
doi:10.1038/nphoton.2013.273
Received
Accepted
Published online

Abstract

Fibre lasers are now associated with high average powers and very high beam qualities. Both these characteristics are required by many industrial, defence and scientific applications, which explains why fibre lasers have become one of the most popular laser technologies. However, this success, which is largely founded on the outstanding characteristics of fibres as an active medium, has only been achieved through researchers around the world striving to overcome many of the limitations imposed by the fibre architecture. This Review focuses on these limitations, both past and current, and the creative solutions that have been proposed for overcoming them. These solutions have enabled fibre lasers to generate the highest diffraction-limited average power achieved to date by solid-state lasers.

At a glance

Figures

  1. Evolution of the average output power of nearly diffraction limited fibre lasers (emitting either a continuous wave or ultrashort pulses) over the past 25 years.
    Figure 1: Evolution of the average output power of nearly diffraction limited fibre lasers (emitting either a continuous wave or ultrashort pulses) over the past 25 years.

    Note that the exponential increase in the average output power stopped around 2010 as the result of encountering a new limitation — mode instabilities. Subsequently, a 20-kW continuous-wave commercial fibre laser was announced in 2013 (green diamond), but its beam quality has yet to be precisely specified.

  2. Schematic of a high-power, double-clad fibre amplifier.
    Figure 2: Schematic of a high-power, double-clad fibre amplifier.

    The signal is coupled in the fibre core, which contains the active material, whereas the pump is coupled in the fibre cladding. This structure allows the pump to be progressively absorbed by the active material in the core as the pump propagates along the fibre. This absorbed pumped energy is used to amplify the signal.

  3. Evolution of pulse energy versus average output power of single-emitter femtosecond fibre lasers since 2002.
    Figure 3: Evolution of pulse energy versus average output power of single-emitter femtosecond fibre lasers since 2002.

    This figure shows that two well-defined types of systems have been developed: those delivering high average powers but low pulse energies (blue), and those delivering high pulse energies but low average powers (red). When attempting to develop systems capable of emitting high pulse energies at high average powers (in the direction indicated by the red arrow), a limit was encountered (black dashed line) because of mode instabilities.

  4. Schematic of mode instabilities.
    Figure 4: Schematic of mode instabilities.

    When a fibre laser is operated below a certain average power threshold (whose value depends on the particular characteristics of the laser), the output beam is stable and has a high quality (left-hand side). However, when the output average power crosses the threshold, the output beam shape starts to fluctuate with time and the beam quality is degraded (right-hand side).

  5. Process leading to the creation of a thermally induced index grating in an active fibre.
    Figure 5: Process leading to the creation of a thermally induced index grating in an active fibre.

    a, When two transverse modes are excited, they create a quasi-periodic intensity pattern along the fibre because of modal interference. b, The interference intensity pattern interacts with the active material, leading to an inversion profile that mimics it and hence has the same periodic features. c, The inversion profile results in a temperature profile with periodic features. d, The three-dimensional temperature profile is transformed into a quasi-periodic index change (grating) via the thermo-optic effect.

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Affiliations

  1. Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany

    • Cesar Jauregui,
    • Jens Limpert &
    • Andreas Tünnermann
  2. Helmholtz Institute Jena, Fröbelstieg 3, 07743 Jena, Germany

    • Jens Limpert &
    • Andreas Tünnermann
  3. Fraunhofer Institute for Applied Optics and Precision Engineering, Albert-Einstein-Strasse 7, 07745 Jena, Germany

    • Jens Limpert &
    • Andreas Tünnermann

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